Unv to unx

Hi Experts,

when we want to Migrate universe  from .unv to .unx   having two options in BO  1) Upgrade management tool 

                                                                                                                                 2) Information design tool (log in IDT file<convert .unv to unx formate)

What is difference between Upgrade management tool and Information design tool convert   from .unv to unx   purpose

Regards,

Rao